1. Field of the Invention
The present invention relates to a rotor structure for an AC generator or a motor and, particularly, to a structure for attaching magnets for preventing the leakage of a magnetic flux between claw-like magnetic poles.
2. Description of the Prior Art
FIG. 13 is a sectional side view showing the constitution of a conventional rotor structure for an AC generator or a motor, FIG. 14 is a perspective view showing the constitution of this rotor, FIG. 15 is an exploded side view of individual parts of the rotor, and FIG. 18 is a sectional view in a radial direction of the claw-like magnetic poles of the rotor.
As shown in FIG. 13, this generator comprises a case 3 consisting of an aluminum front bracket 1 and an aluminum rear bracket 2, a shaft 6 which is installed in the case 2 and one end of which is fitted with a pulley 4, a Randle type rotor 7 fixed to the shaft 6, fans 5 fixed to both end surfaces of the rotor 7, a stator 8 fixed to the inner wall of the case 3, slip rings 9 which are fixed to the other end of the shaft 6 and supply a current to the rotor 7, a pair of brushes 10 in sliding contact with the slip rings 9, a brush holder 11 for storing the brushes 10, a rectifier 12 which is electrically connected to the stator 8 and rectifies an alternating current generated in the stator 8 into a direct current, a heat sink 19 attached to the brush holder 11, and a regulator 20 which is attached to the heat sink 19 and regulates an AC voltage generated in the stator 8.
The stator 8 comprises a stator core 15 and a stator coil 16 which is wound around the stator core 15 and which generates an alternating current by a change in magnetic flux from a rotor coil 13 caused by the rotation of the rotor 7.
The rotor 7 comprises the cylindrical rotor coil 13 for generating a magnetic flux with a current and a pole core 14 which covers the rotor coil 13 and forms a magnetic pole with the magnetic flux of the rotor coil 13.
The pole core 14 consists of a first pole core body 21 and a second pole core body 22 which are mated with each other.
The pole core body 21 and the pole core body 22 are generally made from iron and consist of cylindrical portions 21e and 22e wound with the rotor coil 13 and disk-like base portions 21k and 22k from which the cylindrical portions 21e and 22e project, respectively. The base portions 21k and 22k have at their peripheries a plurality of claw-like magnetic poles 23 and 24 which mate with each other between the outer wall of the rotor coil 13 and the inner wall of the stator 8, respectively.
The thickness and width of each of the claw-like magnetic poles 23 and 24 are large on base portion 21k and 22k sides and become smaller toward the end sides. The inner faces 23a and 24a of the claw-like magnetic poles 23 and 24 are arched in conformity with the peripheral surface of the rotor coil 13 and the outer faces 23b and 24b of the claw-like magnetic poles 23 and 24 are arched in conformity with the inner wall of the stator 8. Each of the claw-like magnetic poles 23 and 24 has two trapezoidal side faces 23c and 24c in a circumferential direction of the rotor 7.
As shown in FIG. 14, a rectangular magnet 30A magnetized to suppress the leakage of a magnetic flux between the opposed side faces 23c and 24c is fixed between the adjacent claw-like magnetic poles 23 and 24. A ring-shaped magnet and a ring-shaped magnet packed in other resin are available in addition to the rectangular magnet 30A to be inserted between the claw-like magnetic poles 23 and 24.
A description is subsequently given of the operation of the generator. A current is supplied from an unshown battery to the rotor coil 13 through the brushes 10 and the slip rings 9 to generate a magnetic flux, whereby the claw-like magnetic poles 23 of the first pole core body 21 are magnetized to an N pole and the claw-like magnetic poles 24 of the second pole core body 22 are magnetized to an S pole. Meanwhile, the pulley 4 is turned by the rotation force of an engine and the rotor 7 is turned by the shaft 6, thereby generating electromotive force in the stator coil 16. The electromotive force of this, alternating current is rectified into a direct current by the rectifier 12, regulated by the regulator 20 and charged into the unshown battery.
However, the following problem may occur. That is, end portions of the claw-like magnetic poles 23 and 24 are moved toward the rotor coil 13 and the stator 8 by centrifugal force generated by the rotation of the rotor 7 and the magnetic attraction force of the stator 8 at the time of power generation. Thereby, a load is applied to the magnet 30A between the claw-like magnetic poles 23 and 24, whereby the magnet 30A may be distorted or broken at about 10,000 to 15,000 rpm.
A countermeasure against this is disclosed by Japanese Laid-open Patent Application No. 11-136913. In this publication, a magnet 30B is formed as shown in FIG. 16, FIG. 17 and FIG. 19. That is, the magnet 30B is fixed to each of the claw-like magnetic poles 23 and 24 in such a manner that it covers the inner faces 23a and 24a and the side faces 23c and 24c of the claw-like magnetic poles 23 and 24. A space 25 is formed between the adjacent magnets 30B. Thereby, a set of the claw-like magnetic pole 23 and the magnet 30B and a set of the claw-like magnetic pole 24 and the magnet 30B move independently, thereby preventing the application of a load to the magnet 30B and the breakage of the magnet 30B.
However, in the prior art generator, as shown in FIG. 19, the magnets 30B are provided for the claw-like magnetic poles 23 and 24 in such a manner that they cover the inner faces 23a and 24a and side faces 23c and 24c of the claw-like magnetic poles 23 and 24. Therefore, as shown in FIG. 18, compared with the rectangular magnet 30A interposed between the adjacent claw-like magnetic poles 23 and 24, the claw-like magnetic poles 23 and 24 are not cooled well because the magnets 30B surround the claw-like magnetic poles 23 and 24.
Therefore, the coolability of the magnet 30B deteriorates and the temperature of the magnet 30B rises, thereby reducing magnetic force. Further, when the temperature rises and becomes higher than the thermal deformation temperature of the magnet 30B, the magnet 30B is broken.
The present invention which has been made to solve the above problems improves the coolability of magnets provided to suppress the leakage of a magnetic flux between claw-like magnetic poles and prevents a reduction in magnetic force to suppress deterioration in the output of an AC generator.
According to a first aspect of the present invention, there is provided a rotor structure comprising a rotor coil for generating a magnetic flux with a current, a pole core which is provided to cover the rotor coil and consists of a first pole core body and a second pole core body, each having claw-like magnetic poles which are situated to mate with each other at positions where they cover the peripheral surface of the rotor coil, magnets which are provided on both sides of each of the claw-like magnetic poles and suppress the leakage of a magnetic flux between the side faces of the adjacent claw-like magnetic poles, and metal holding members each of which fixes the magnets to each of the claw-like magnetic poles in such a manner that it covers the magnets together with the claw-like magnetic pole and radiates heat transmitted to the claw-like magnetic pole at the time of power generation to cool the magnets.
According to a second aspect of the present invention, there is provided a rotor structure, wherein an exposing portion for exposing part of the peripheral surface of the magnet is formed in the holding member to contact the peripheral surface of the magnet to cooling air.
According to a third aspect of the present invention, there is provided a rotor structure, wherein the surface area of the holding member is increased to improve its coolability.
According to a fourth aspect of the present invention, there is provided a rotor structure, wherein projecting pieces are formed on the holding member or the holding member is formed wavy or uneven to increase its surface area in order to improve its coolability.
According to a fifth aspect of the present invention, there is provided a rotor structure, wherein the root portion or end portion of the holding member is extended in the axial directions of the first and second pole core bodies and projected from the claw-like magnetic poles.
According to a sixth aspect of the present invention, there is provided a rotor structure, wherein the extension of the root portion or end portion of the holding member projects from the end surface of the first or second pole core body.
According to a seventh aspect of the present invention, there is provided a rotor structure, wherein a cooling fan is formed on the extension of the root portion or end portion of the holding member which projects from the end surface of the pole core
The above and other objects, features and advantages of the invention will become more apparent from the following description when taken in conjunction with the accompanying drawings.